A bomb is any of a range of explosive devices that typically rely on the exothermic chemical reaction of an explosive material to produce an extremely sudden and violent release of energy. The word comes from the Greek word βόμβος (bombos), an onomatopoetic term with approximately the same meaning as "boom" in English. A nuclear weapon employs chemical-based explosives to initiate a much larger nuclear-based explosion.

The term "bomb" is not usually applied to explosive devices used for civilian purposes such as construction or mining, although the people using the devices may sometimes refer to them as bombs. The military use of the term "bomb", or more specifically aerial bomb, typically refers to airdropped, unpowered explosive weapons most commonly used by air forces and naval aviation. Other military explosive devices not classified as "bombs" include grenades, shells, depth charges (used in water), warheads when in missiles, or land mines. In unconventional warfare, "bomb" can refer to any of a limitless range of explosive devices used as boobytraps or offensive weapons.

Effects

Detonation causes injury and/or death within the blast radius through three distinct yet inter-related phenomena: shock wave (a.k.a. detonation wave, pressure wave or overpressure), thermal wave and fragmentation.

A shock wave is produced when an explosive event suddenly displaces a volume of air spherically outward from the point of detonation. At its initial creation this phenomenon might best be visualized as a round, thick "shell" of highly compressed air enclosing a vacuum. This shell of pressurized air will expand outward at a speed described by the Chapman-Jouguet condition, typically several to many times the speed of sound.

Even brief exposure to overpressure conditions can cause severe damage, crush injury and death. 1psi overpressure can shatter windows, 5psi can rupture eardrums and shatter a 12-inch concrete wall, and 15psi can cause severe lung damage. Shock waves dissipate as they expand, and the greatest defense against shock injuries is distance from the source of shock. As a point of reference, the overpressure at the Oklahoma City bombing was estimated in the range of 4000psi.

Shock waves produced by explosive events actually have two distinct components, the positive and negative wave. The positive wave shoves outward from the point of detonation, followed by the trailing vacuum space which "sucks back" towards the point of origin as the shock bubble collapses back on itself. This is most clearly observed in footage from the Trinity nuclear test where both the positive and negative effects on buildings are evident.

A thermal wave is created by the sudden release of heat caused by an explosion. Military bomb tests have documented temperatures of 3000 to 4500˚F. While capable of inflicting severe to catastrophic burns and causing secondary fires, thermal wave effects are considered very limited in range compared to shock and fragmentation. This rule has been challenged, however, by military development of thermobaric weapons, which employ a combination of negative shock wave effects and extreme temperature to incinerate objects within the blast radius.